The invention relates to a four-stroke internal combustion engine with at least two inlet valves and an inlet flow path with at least two inlet ports per cylinder which branch off from a common inlet pipe and are guided separately up to the inlet valves and of which at least one inlet port is designed as a charge loading port and at least one inlet port as a volumetric port, with a throttle device for volumetric control being provided in the inlet flow path and the inlet flow path being connected with a fuel supply device.
An internal combustion engine of the kind mentioned above is known from AT 402 535 B. In order to achieve a strong swirl of the charge in the combustion chamber under partial load without impairing the charge admission under full load due to adverser flow coefficients and thus impairing the engine""s performance, the known internal combustion engine is provided with a charge loading port and a volumetric port. The fuel is injected via an injection apparatus into both inlet ports in the direction of the admission openings indirectly by means of an injection device arranged in the zone of the port separating wall between the two inlet ports. The mixture in the combustion chamber can be influenced by means of a throttle valve arranged in the volumetric port. Thus it is possible to produce in the combustion chamber a stratification in order to form an explosive, relatively rich mixture in the region of the spark plug with a generally lean mixture otherwise. This allows fulfilling particularly strict exhaust gas regulations at low fuel consumption.
Since the arrangement of the inlet port and the supply of fuel by means of indirect injection is relatively complex, the known system is particularly suitable for multi-track motor vehicles. Injection systems have not proven their worth in single-track motor vehicles, particularly where small-volume motorcycles are concerned, because the achieved fuel savings were far below expectations. Moreover, injection systems require a relatively large amount of control and energy, which has a negative effect on the size, weight and costs of the internal combustion engine.
It is the object of the present invention to avoid such disadvantages and to improve the exhaust gas quality in an internal combustion engine of the kind mentioned above in the simplest possible manner. At the same time it is the object to achieve the lowest possible fuel consumption.
This is achieved in accordance with the invention in that the fuel supply device is formed by a joint carburetor for both inlet ports, with preferably the carburetor being arranged in the zone of the branching of the inlet ports from the inlet pipe. As a result of the combination between load charging port, volumetric port and a fuel supply device arranged as a conventional carburetor, it is possible in a very simple manner to achieve a controlled combustion in the combustion chamber with very low emission values and very favorable fuel consumption. By using a conventional carburetor with a double inlet port configuration with a volumetric port and a charge loading port, it is possible to make do without any complex electric and electronic devices. Thus, one can omit complex control and regulation apparatuses for injecting the fuel, including the higher provision of energy. Carburetor technology moreover offers the highest possible reliability and the additional advantage that the dimensional volume, weight and costs of the internal combustion engine can be kept very low.
In order enable the optional performance of a stratification in the combustion chamber, it is provided for in a further embodiment of the invention that during the opening of the throttle device the charge loading port can be opened at first and the volumetric port thereafter.
The charge loading port has the task of providing the charge in the combustion chamber with a momentum about the cylinder axis. It can be arranged as a tangential or spiral port.
The carburetor can be formed by a slide valve carburetor, constant-pressure carburetor or a rotating throttle valve carburetor. In the case of a slide valve carburetor or a constant-pressure carburetor, the carburetor slide valve is arranged in the zone of the beginning of one port separating wall between the two inlet ports and forms a port separating member. The carburetor slide valve thus produces a port separation, so that the two inlet ports are released successively during a travel process of the slide valve. In this case the carburetor slide valve thus forms the throttle device. The throttle device can additionally be provided with throttle valve in one or both of the inlet ports.
If one throttle valve is arranged in each of the separate inlet ports, the throttle valves are preferably opened in a register-like manner one after the other.
If the carburetor is arranged as a rotating throttle valve carburetor, a throttle valve is provided for each inlet port. The two throttle valves open the two inlet ports one after the other in a register-like manner and thus form the throttle device.
In order to achieve a maximum output yield under full load, it is particularly advantageous that the carburetor is provided with a full-load power jet which is arranged in the direction of flow to the volumetric port, so that the fuel jet predominantly enters the volumetric port.
It is provided for in a further development of the invention that at least one self-opening diaphragm valve is provided in the port separating wall between the two inlet ports downstream of the throttle device, which diaphragm valve connects the two inlet ports and which preferably produces the flow connection from the charge loading port to the volumetric port in the case of pressure difference. This allows an improvement in the charging of the cylinder.
It is very advantageous for improving the exhaust gas quality when at least one exhaust gas return conduit opens into at least one inlet port, preferably into the charge loading port. It can be provided for in this respect that the exhaust gas return can be actuated by a slide valve which is preferably coupled with the control for the throttle device.
It can be provided for on the basis of the concept that the charge loading port which is arranged as a tangential or swirl port is provided with a larger length than the volumetric port. If the charge loading port is arranged as a tangential port, it is provided with only a low curvature and is strongly inclined towards the valve axis and produces a flow which hits the cylinder wall tangentially and leads to the formation of a strong swirling movement in the cylinder. The volumetric or neutral port is provided with a stronger curvature as compared with the tangential port, but shows a lower inclination towards the valve axis. It produces a stream directed approximately against the centre of the cylinder which neither produces a marked swirling movement, nor a tumble movement.
The throttling of the volumetric port ensures that the admission of the charge from this port occurs with a lower impulse into the cylinder chamber than the air supplied by the tangential port. The overall flow field in the cylinder chamber is thus dominated by the unthrottled tangential port. The charge loading thus produces a rapid, stable and even combustion. This leads to a lower susceptibility to engine knock despite higher compression. This creates the prerequisites for achieving high thinnability in order to achieve lower fuel consumption. At the same time, compatibility for higher exhaust gas return rates is increased, thus enabling a considerable decrease in NOx emissions.
In order to produce the described charge movement in the combustion chamber it is advantageous when at least two inlet ports are arranged above one another in the zone of the carburetor, with the volumetric port preferably being arranged above the charge loading port.
In order to provide the internal combustion engine as compact as possible, the carburetor is arranged as a cross flow carburetor. Notice should be taken that the inlet ports are provided between the carburetor and the inlet valves with a horizontal guidance, preferably a slope.
It can further be provided within the scope of the invention that at least one inlet port, preferably the charge loading port, is provided with at least one stall edge. This helps prevent that a fuel wall film produced by the fuel introduction is directed onto the cylinder wall. It is particularly advantageous when the stall edge is arranged on a side of the inlet port which is adjacent to the wall of the cylinder. As the fuel wall films occur cumulatively at the outer side of the port curvatures, it is preferably provided that the stall edge is arranged on the outer side of an arc-shaped section of the inlet port.
In order to enable utilising resonance effects of the inlet ports for charging the cylinder in the partial load range in particular, it is advantageous when a port loop is arranged in one of the inlet ports. The port loop is preferably arranged in the charge loading port and is provided with a loop-like shape. In order to enable the charge to be supplied over the shortest possible path to the cylinder, the port loop can be by-passed via a by-pass opening in the zone of the port loop crossing, with the by-pass opening being controlled by a by-pass valve depending on the engine load. The by-pass valve is designed in a particularly simple arrangement as a membrane valve which opens and closes the by-pass valve depending on the pressure difference between the loop entrance and the loop exit.